A dust collector of the above-mentioned type is previously known by the U.S. Pat. No. 3,146,081. In that apparatus the dust-laden air is taken into the coarse separating tube through a duct which extends radially out from the cylindrical tube wall and enters the tube at a point situated below a conical deflector which converges downwardly and is attached to the inside of the tube in order to divide the same in upper and lower chambers. By this design the air taken in will get a turbulent uncontrolled movement which results in a very great fraction of the dust or solid components in the air accompanying the same past the deflector and into the subsequent filter unit. Therefore the latter tends to be rapidly clogged. Further the filter unit consists of a single bag which either--in case it is manufactured with a loose fibre structure--will let a great fraction of fine particles through, or--in case it is manufactured with a fine fibre structure--is clogged extremely rapidly.